The present application relates generally to systems and/or apparatus for improving the efficiency and/or operation of turbine engines and/or industrial machinery, which, as used herein and unless specifically stated otherwise, is meant to include all types of engines and, particularly, turbine or rotary engines, including gas turbine engines, aircraft engines, power generation engines, steam turbine engines and others. More specifically, but not by way of limitation, the present application relates to methods, systems, and/or apparatus pertaining to an improved brush seal between the stationary and rotating parts of a turbomachine such as a steam turbine.
During operation of a turbomachine, a high pressure region is created at an upstream side and a low pressure region is created at a downstream side of stationary and rotating parts of the turbomachine. For free rotation of the rotating parts, clearance gaps are left between the stationary and rotating parts. However, if these gaps are not properly sealed, flow leakage may occur from the high pressure region to the low pressure region. This leakage through the stationary and rotating parts of the turbomachine may have a significant effect on the performance of the turbomachine.
Over the years, different concepts have been used for sealing the clearance gap between the stationary and rotating parts. These include non-contact type labyrinth seals and contact type brush seals, both of which are widely used in turbomachines to provide dynamic seals between the rotating and static components. The labyrinth seal either requires a large physical clearance to avoid contact, or has initial rubs, which may result in blunted-teeth and subsequently cause substantial leakage. On the other hand, the effective clearance in the brush seal is substantially less than in the conventional labyrinth seal, as the brush seal maintains contact with the rotor during a majority of the rotor's operating cycle. However, pressure drop across the bristles in the brush seal may result in a stiff bristle pack, which may lead to heating of the rotor, and may subsequently cause high vibration. Moreover, the bristles tend to deform under the influence of the pressure drop. To counter this effect, generally a pressure plate may be used to provide lateral support for the bristles on the downstream side, i.e., the low pressure side of the bristles. However, the pressure drop that exists across the bristle pack may cause the bristles to have a frictional engagement with the face of the pressure plate, and thus increases bristle stiffness and causes wear in case of rotor excursion. Moreover, the restoring forces provided by the inherent resilience of the bristles and other such forces are also inhibited, which further affects sealing performance of the brush seal.
The frictional engagement may be reduced by achieving a configuration that results in balanced pressure on either sides of the bristle pack. Several prior attempts have been made to introduce pressure balancing features in the brush seals. One such solution involves positioning the pressure plate interposed between the bristle layer and the low pressure region such that the arrangement defines at least one pocket formed between the bristle pack and the pressure plate. The benefit can be maximized by making the pocket wide enough to cover most of the radial length of the pressure plate. However, such a pocket will compromise the support provided by the pressure plate. One solution is to divide the pocket into multiple grooves such that improved support for the bristles is provided. However, the lands provided between the grooves generally prevent pressure communication between the grooves. Holes may be used to provide communication tunnels between the grooves, or even connection to upstream pressure directly. However, such designs generally results in a overly thick pressure plate, made so to accommodate the necessary holes and passageways. In addition, such features generally create manufacturing difficulties or, at minimum, increased costs. More often, the pressure balancing features, i.e., the multiple cavities or grooves, end up negatively affecting the support the pressure plate provides to the bristle pad. And, narrow land portions cause damage to the bristles, cutting or permanently bending them. These limitations, in turn, limit the use of the brush seal at higher-pressure differentials and/or higher temperatures.
As a result, there is a need for improved brush seals that are cost-effective while also being effective at preventing leakage between the stationary and rotating parts of the turbomachines and other industrial machinery.